Ultra wideband (UWB) technology uses base-band pulses of very short duration to spread the energy of transmitted signals very thinly from near zero to several GHz. UWB technology is presently in use In military applications and techniques for generating UWB signals are well known. Commercial applications will soon become possible due to a recent decision announced by the Federal Communications Commission (FCC) that permits the marketing and operation of consumer products incorporating UWB technology.
The key motivation for the FCC's decision to allow commercial applications is that no new communication spectrum is required for UWB transmissions because, when they are properly configured, UWB signals can coexist with other application signals in the same spectrum with negligible mutual interference. The FCC has specified emission limits for UWB applications to prevent Interference with other communication systems.
The emission profile of a UWB signal can be determined by examining Its power spectral density (PSD). Characterization of the PSD of a “Time-Hopping Spread Spectrum” signaling scheme in the presence of random timing jitter using a stochastic approach is disclosed in an article by Moe et al. titled “On the Power Spectral Density of Digital Pulse Streams Generated by M-ary Cyclostationary Sequences In the Presence of Stationary Timing Jitter.” See IEEE Tran. on Comm., Vol. 46, no. 9, pp. 1135-1145, September 1998. According to this article, the power spectra of UWB signals consists of continuous and discrete components. Discrete components create peaks in the PSD that may exceed the FCC emission limits even when the continuous components are well below these limits.
There is an ever present desire to increase the communication distances of communication systems. One way to Increase communication distance is to increase the power used for transmissions. To increase transmission power while still conforming to the FCC emission limits for UWB signals, it is desirable to reduce the discrete components so that overall power can be increased while still conforming to the FCC emission limits for UWB signals. In traditional communication systems, scramblers are commonly used to reduce discrete components (i.e., data whitening). These scramblers, however, are insufficient for reducing discrete PSD components In UWB communication systems, e.g., due to their high pulse repetition frequency (PRF), i.e., about 100 Mbps to 500 Mbps, and their time division multiple access (TDMA) frame structure. Accordingly, improved methods and apparatus for reducing discrete PSD components of UWB signals are needed. The present invention fulfills this need among others.